This work attempts to measure the rate of aqueous humor flow in humans by determining the rate of loss of fluorescein from the eye after iontophoresis of fluorescein into the cornea. The aqueous humor flow is also calculated from tonographic results in the same individuals, allowing a comparison of the two methods. Individuals with normal, low, or high intraocular pressure are studied to examine the effect of intraocular pressure on aqueous flow. The accuracy of the aqueous flow rate measured by fluorophotometry was evaluated in freshly enucleated monkey eyes. The calculated flow rate averaged 5 percent lower than the known perfusion rate.